WebKitGTK experimental runs missing since August 13

[KyleJu]

The last run for WebKitGTK Experimental was August 13

https://wpt.fyi/runs?label=master&label=experimental&max-count=100&product=chrome&product=edge&product=firefox&product=safari&product=webkitgtk

@clopez could you take a look please?

[clopez]

The problem has been caused because an upgrade on the toolchain on the server generating the webkitgtk built-products also upgraded the libstdc++ version on the container and therefore the built-products generated are now incompatible with Ubuntu-20.04

Building webkitgtk requires gcc >= 11 nowadays and that is an issue as it is becoming increasingly hard to keep providing build-products for such old distro.

I think we should look into upgrading the docker container that is used for the WPT CI tests at taskcluster. Related: #43361

[clopez]

We are going to start providing a generic bundle that can work on any distro and has all the bleeding edge features enabled instead of providing a bundle with several features disabled to make it compile on an ancient distro like Ubuntu-20.04
To achieve that we will bundle all the required libraries instead of depending on the distro libraries.

I will submit a patch here to switch the WPT tooling to pull this new bundle once ready and that should make the webkitgtk runs work back as expected.

Work for shipping the new bundle tracked at https://bugs.webkit.org/show_bug.cgi?id=280523 and the bugs linked there in see-also